Adolescence is an important developmental period characterized by rapid changes in multiple domains, including maturation of the brain's prefrontal cortex, increases in planning and cognitive control, and also a large increase in rates of anxiety and depression. Deficits in control and planning have been identified as a risk factor for mental illness, including depression and anxiety. One aspect of control that is understudied but likely affects risk for depression and anxiety, is the ability to quickly and efficiently selec among competing options when planning or working towards a goal. Such selection can be difficult for anyone, but is especially so for individuals with elevated levels of anxiety or depression, leading to problems in planning and decision-making. To date, these issues have primarily been studied in adults. However, it is important to understand how these abilities develop during adolescence because that is the developmental time period in which many aspects of mental illness first appear. The proposed research builds upon an innovative and integrative model of how such selection abilities are accomplished. It examines this issue at multiple units of analysis, linking a) neurochemistry of the brain, to b) activation of specific brin regions, to c) behavioral performance on tasks requiring selection to d) self-report of the ability to select amongst alternatives in daily life. This proposal brings together a multi-disciplinary team of scientists that articulated and tested the original model in adults (cognitive and developmental neuroscientists, and a physicist with expertise in brain imaging) with a clinical scientist with expertise in development of anxiety and depression during adolescence. The project leverages a highly retained sample of youth and their caregivers who have been prospectively followed for 5 years with extensive evaluation of psychopathology, but have not previously undergone neuroimaging or evaluation of planning or control. The project will test 144 youth (72 middle and 72 older adolescents) and 72 adults both at an initial time point and then two years later. This project aims to determine the development of biobehavioral mechanisms for selection in adolescence and adulthood (Aim 1), associations between selection mechanisms and anxiety and depression (Aim 2), and how these selection mechanisms over time may predict changes in psychopathology and/or vice versa (Aim 3). The proposed research will make a significant, innovative impact by providing information about important processes that develop during adolescence, and their relationship to the onset of mental illness. The data provided by the project will help break new ground and advance the field's understanding of developmental changes in the interplay of control and planning with mental health during the critical adolescent period.